The origin of the collagen polymorphism observed in human pulmonary fibrosis remains obscure. To determine whether changes in the proportions of Type III and Type I collagen observed in whole lungs reflect phenotypic shifts in individual lung cell types, we have isolated a number of fibroblast cell lines from normal adults and from patients with pulmonary fibrosis. Collagen types are separated and quantitated using carboxymethyl cellulose chromatography and acrylamide gel electrophoresis.